Andromeda Galaxy
Andromeda Galaxy The Andromeda Galaxy ( /ænˈdrɒmədə/) is a spiral galaxy approximately 2.5 million light-years from Earth[4] in the constellation Andromeda. It is also known as'Messier 31', M31, or NGC 224, and is often referred to as the Great Andromeda Nebula in older texts. Andromeda is the nearest spiral galaxy to the Milky Way, but not the closest galaxy overall. It gets its name from the area of the sky in which it appears, the Andromeda constellation, which was named after the mythological princess Andromeda. Andromeda is the largest galaxy of the Local Group, which consists of the Andromeda Galaxy, the Milky Way, the Triangulum Galaxy, and about 30 other smaller galaxies. Although the largest, Andromeda may not be the most massive, as recent findings suggest that the Milky Way contains more dark matter and may be the most massive in the grouping.[10] The 2006 observations by the Spitzer Space Telescope revealed that M31 contains one trillion (1012)stars,[7]: at least twice more than the number of stars in our own galaxy, which is estimated to be c. 200–400 billion.[11] Andromeda is estimated to be 7.1×1011 solar masses.[2] In comparison a 2009 study estimated that the Milky Way and Andromeda are about equal in mass,[12] while a 2006 study put the mass of the Milky Way at ~80% of the mass of Andromeda. The Andromeda Galaxy and the Milky Way are expected to collide in perhaps 4.5 billion years. At an apparent magnitude of 3.4, the Andromeda Galaxy is notable for being one of the brightest Messier objects,[13] making it visible to the naked eye on moonless nights even when viewed from areas with moderate light pollution. Although it appears more than six times as wide as the full Moon when photographed through a larger telescope, only the brighter central region is visible to the naked eye or when viewed using a binoculars or a small telescope. Observation History The Persian astronomer Abd al-Rahman al-Sufi wrote a tantalizing line about the chained constellation in his Book of Fixed Stars around 964, describing it as a "small cloud".1415 Star charts of that period have it labeled as the Little Cloud.15 The first description of the object based on telescopic observation was given by German astronomer Simon Marius15 in 1612. Charles Messier catalogued it as object M31 in 1764 and incorrectly credited Marius as the discoverer, unaware of Al Sufi's earlier work. In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of the M31. He believed it to be the nearest of all the "great nebulae" and based on the colour and magnitude of the nebula, he incorrectly guessed that it was no more than 2,000 times the distance of Sirius.16 William Huggins in 1864 observed the spectrum of M31 and noted that it differed from a gaseous nebula.17 The spectra of M31 displayed a continuum of frequencies, superimposed with dark absorption lines that help identify the chemical composition of an object. The Andromeda nebula was very similar to the spectra of individual stars, and from this it was deduced that M31 had a stellar nature. In 1885, a supernova (known as "S Andromedae") was seen in M31, the first and so far only one observed in that galaxy. At the time M31 was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova, and was named accordingly "Nova 1885".18 The first photographs of M31 were taken in 1887 by Isaac Roberts from his private observatory in Sussex, England. The long-duration exposure allowed the spiral structure of the galaxy to be seen for the first time.19 However, at the time this object was still commonly believed to be a nebula within our galaxy, and Roberts mistakenly believed that M31 and similar spiral nebulae were actually solar systems being formed, with the satellites nascent planets. The radial velocity of this object with respect to our solar system was measured in 1912 by Vesto Slipher at the Lowell Observatory, using spectroscopy. The result was the largest velocity recorded at that time, at 300 kilometres per second (190 mi/s), moving in the direction of the Sun.20 Gallery 260px-Makemake hubble.png 2003 EL61.jpg 200px-Stylised Lithium Atom.svg.png Oxygen8.jpg 120px-Carbon-monoxide-3D-vdW.png 250px-Diamond-and-graphite-with-scale.jpg 220px-Insulincrystals.jpg 220px-Halite-36944.jpg 200px-VFPt dipole electric.svg.png Dipole small.jpg 340px-Light-wave.svg.png 324px-Light spectrum.svg.png 300px-Atmospheric electromagnetic opacity.svg.png 220px-Sine wavelength.svg.png 300px-Sombrero Galaxy in infrared light (Hubble Space Telescope and Spitzer Space Telescope).jpg 300px-Alfa beta gamma radiation penetration.svg.png 300px-NGC 4414 (NASA-med).jpg 220px-Bohr atom model English.svg.png 220px-Cyclotron motion wider view.jpg Atom.jpg Research4.png 220px-Alpha Decay.svg.png 220px-Moon gamma rays egret instrument cgro.jpg Swift-gamma-ray-lg.jpg 220px-Electromagneticwave3D.gif 220px-VFPt Solenoid correct2.svg.png EM-spectrum.png 220px-Blue sun.jpg 300px-Keplers supernova.jpg 250px-Andromeda Galaxy (with h-alpha).jpg Images.jpg AlphaCentauri 468x318.jpg Alpha cen poss big.gif Solar system.jpg 15750195.jpg 170px-William Herschel01.jpg 240px-Uranus2.jpg 220px-Saturn from Cassini Orbiter (2007-01-19).jpg 280px-Saturn during Equinox.jpg 250px-Mars Valles Marineris.jpeg 1100px-Victoria Crater, Cape Verde-Mars.jpg 220px-Jupiter interior.png 240px-Jupiter by Cassini-Huygens.jpg 220px-Mercuryorbitsolarsystem.gif 240px-Mercury in color - Prockter07 centered.jpg Earth mark1 jestr.jpg 250px-The Earth seen from Apollo 17.jpg Earth-1.jpg 220px-Venus globe.jpg 250px-Venus-real.jpg Category:Community Category:Category templates Category:Content Category:Template documentation Category:Site maintenance Category:Article management templates Category:Policy Category:Watercooler Category:Hidden categories Category:Organization Category:Site administration